1. Field of the Invention
This invention relates to a shock absorbing arrangement for a marine outboard drive and more particularly to a shock absorbing arrangement for a compact tilt adjustment system that is particularly well suited for small outboard drive.
2. Description of Related Art
In a wide variety of outboard drives, both outboard motors and the outboard drive section of and inboard/outboard drive, a hydraulic tilt adjustment mechanism supports the outboard drive for tilting movement relative to a hull of an associated watercraft about a substantially horizontally disposed tilt axis. The tilt adjustment mechanism generally has a shock absorbing arrangement in case the outboard drive strikes an underwater obstacle so as to protect the drive from being seriously damaged.
FIGS. 1 and 2 illustrate an exemplary fluid motor assembly with a shock absorbing arrangement of a conventional tilt adjustment mechanism. FIG. 2 is a cross-sectional view taken along the line 2—2 in FIG. 1.
The fluid motor assembly, indicated generally by the reference numeral 1 in FIGS. 1 and 2, has a cylinder 2. The lower end 3 of the cylinder 2 is connected to a clamping bracket (not shown) that is affixed to an associated watercraft. The clamping bracket supports a swivel bracket (not shown) for pivotal movement about a horizontally disposed axis. A plug 4 is provided for closing the upper end of the cylinder 2. The cylinder 2 slidably supports a piston 5 that defines an upper chamber 6 and a lower chamber 7. A piston rod 8 is affixed to the piston 5 with a bolt 9 and the rod 8 extends through the upper chamber 6 outwardly through the plug 4. A washer 10 is interposed between the piston 5 and the bolt 9. The washer has a flange portion 11 that acts as a seat for a check valve assembly described later.
An upper end 12 of the piston rod 8 is connected to a swivel bracket that supports a drive unit (not shown) for pivotal movement about a vertically disposed axis. An opening 13 is provided at the upper portion of the cylinder 2 that is immediately below the plug 4, and then through the upper chamber 6 is connected to a fluid supply and control system (not shown). Meanwhile, another opening 14 is provided at the lower portion of the cylinder 2 that is immediately above the lower end 3 and thereby the lower chamber 7 is connected to the fluid supply and control system also. In other words, the upper chamber 6 and the lower chamber 7 are connected with each other through the fluid supply and control system. The hydraulic assembly 1 is filled with a hydraulic fluid. This hydraulic fluid is moved from the upper chamber 6 to the lower chamber 7 or vice versa by the fluid supply and control system and hence the piston rod 8 may extend until the piston 5 contacts the plug 4 and retract until the piston 5 contacts the lower end 4. By these movements, the outboard drive is tilted up or tilted down.
The piston 5 has a plurality of hollows 15 that are disposed at the periphery of the piston 5 at even intervals. These hollows 15 open to the lower chamber 7. The individual hollows 15 are also connected to the upper chamber 6 through apertures or passages 16. The arrangement of these apertures 16 is best seen in FIG. 2. A plurality of check valve assembly assemblies 17 are accommodated in the individual hollows 15. The check valve assembly 17 consists of a ball 18, a retainer 19 and a spring 20. The ball 18 is seated at a valve seat 21 formed at an upper end of the respective hollow 15. The diameter of the ball 15 is larger than the diameter of the valve seat 21. The spring 20 is placed between the retainer 19 that retains the ball 15 and the flange portion 11 of the washer 10 so that the ball 18 is urged against the valve seat 21 to close off fluid flow through the respective check valve assembly between the upper chamber 6 and the lower chamber 7.
When an underwater obstacle, such as a drift wood or a rock, is struck by the drive unit with sufficient force, the piston rod 8 will exert sufficient force on the piston 5 so as to overcome the action of the check valve assemblies 17. That is, the sufficient force on the piston 5 moves each ball 18 to an open position against the bias of the corresponding spring 20. Thus, the fluid in the upper chamber 6 can flow into the lower chamber 7 through the aperture 16 and the hollow 15. The flow of the fluid from the upper chamber 6 to the lower chamber 7 permits the piston 5 to move upwardly as indicated with the arrow 22 and, thus, allows the drive unit to pop up.
As described above and seen in FIGS. 1 and 2, the plurality of check valve assemblies 17 are provided at the periphery of the piston 5 so as to surround the connecting bolt 9. A relatively small outboard drive, however, can accommodate only a slim cylinder. Such a slim cylinder has a smaller diameter piston that often does not have enough space to accommodate the check valve assemblies around a connecting bolt. Because a piston rod should have almost the same thickness as that in a larger outboard drive for keeping its stiffness, little space exists to accommodate such value assemblies on a smaller diameter piston.
One shock absorbing arrangement that may resolve the problem noted above is disclosed in the U.S. Pat. No. 5,262,843. The construction of this cylinder, however, is complicated and thus costly to produce.